Voltage-dependent K+ channels regulate the excitability of neurons and serve as receptors for a variety of synthetic drugs and natural toxins. Recently, cDNAs encoding rat brain K+ channels have been isolated. When expressed in Xenopus oocytes different K+ channel clones have different pharmacological profiles, but little is known about the mechanisms of action of pharmacological agents in brain K+ channels or their binding sites on the channel proteins. We propose to use a combination of electrophysiological and recombinant DNA methods to identify and probe regions of the K+ channel primary structure which interact with toxins and drugs. Binding sites will be probed by site-directed mutagenesis and mechanisms of action will be investigated by voltage-clamp electro- physiology in the Xenopus oocyte expression system. Expression of pure channel isoforms in oocytes provides a unique opportunity for studying drug mechanisms unencumbered by the usual complexities arising from the presence of heterogenous K+ channel subtypes in excitable cells. The results of this study should provide insight into K+ channel surface topography, help to elucidate the structural basis for drug and toxin specificity, and guide the development of therapeutic agents targeted against K+ channels.